Flexible disc magnetic recorders, although known in a general way for some time in the past, are more recently coming into much more prominent and frequent use, particularly in digital data storage applications.
The type of disc media most frequently encountered at this time is generally as shown in U.S. Pat. No. 3,668,658 and includes a thin, limply flexible magnetic recording disc generally having the characteristics of magnetic tape, which is permanently enclosed within a generally square (or rectangular) envelope, which is itself of flexible sheet plastic or the like, although being less flexible than the disc and, with the enclosed disc, making up an assembly that is self-supporting, or very nearly so.
The typical manner of using such disc assemblies is to restrain the corners of the rectangular disc enclosure or jacket and rotate the disc within its enclosing jacket, by engaging the center part of the disc, which is exposed through an opening in the side of the jacket. The jacket, or envelope, also defines a radial opening through which the recording disc is exposed, for access by the recording head, which by traversing the disc radially while it is rotated may thus address the same at any point on its surface.
The proper transducing relationship of the recording head to the disc has been the subject of considerable investigation and effort, and certain of the considerations involved are shown in U.S. Pat. No. 3,688,285, which shows a typical transducing relationship, in which the head actually protrudes into the plane of the disc when the same is rotated, thereby creating a moving dimple-like elastic deformation under such conditions. Typically, the extremely close, intimate proximity required for proper transducing operation (believed by some to be an air film on the order of a few microinches thick, while regarded by others as being direct sliding contact) is maintained, at least for the jacketed type of disc referred to above, by pressure pads; most usually, a felt or other such cushioning pad which is located directly on the opposite side of the disc from the transducing head, and which in effect presses the disc against the head. Such a practice, while regarded by many as being essential to proper recording operation, does severly limit the operational flexibility of recorders designed to operate with such discs, since the oppositely-disposed transducing head and pressure pad essentially use all of the allowable access area to the disc which is provided by the jacket. Consequently, such recorders typically have allowed for recording only on one side of the disc, even though commercial discs are manufactured with the capability of recording on each side. In present equipment, however, such recording can be accomplished only by physically withdrawing and reversing the disc assembly.
Accordingly, recorders manufactured and used heretofore have not taken full advantage of the operational flexibility or usefulness made possible by the disc assemblies themselves; furthermore, achieving and maintaining proper transducing relationship of the head to the disc has been a source of constant experimentation and change, believed in large part to result from operation which is basically unsatisfactory in nature.